The present invention relates to a drilling tool. More particularly, it relates to a drilling tool or bit which has a shaft member, a crown drilling member detachably connected with the shaft member and a center drilling member detachably connected with the shaft member and located in the interior of the crown drilling member.
Such drilling tools are known in the art and disclosed for example in the German Offenlegungsschrift No. 2,602,238. The center drilling member in the known drilling tool is screwed in a coaxial bore of the shaft member. The drilling tool operates in a satisfactory manner. It has been shown, however, that the drilling process in accordance with the diameter of the core drilling element can be considerably increased when after the initial drilling the central drilling element is removed from the tool. Then the entire impact energy of the hard alloy cutting edges of the ring-shaped crown drilling member can be transmitted to the lock to be drilled. This is true also for known drilling tools. It has been however recognized that many users of the drilling tool do not remove the center drilling means from the tool after the termination of the step of initial drilling.